An Investigation into the Stephens–Castro Synthesis of Dehydrotriaryl[12]annulenes: Factors Influencing the Cyclotrimerization

Abstract

Detailed investigation into the CuX/base/phosphine modified Stephens–Castro syntheses of dehydrotriaryl[12]annulenes 1–3 have shown that cyclization is suppressed by excess CuX, strong donor ligands, high dilution conditions, and thermally unstable ethynylcuprate monomers. Surprisingly, intermediate dimer 16 plays only a minor role in the formation of 2 and 4. Overall, our findings are consistent with a cyclization pathway governed more by the nature of prior self-association of the ethynylcuprate monomers. Crystallographic characterization of tetrameric by-product 4, is also reported and revealed that it assembles into tubular stacks in the solid state.